"Our justice system is under attack," said Sen. Richard Blumenthal, a Connecticut Democrat, on Tuesday.

Sen. Dick Durbin, the second ranking Democrat in the Senate, called Trump's actions, including firing former FBI Director James Comey and his tweets that criticized Sessions, "unprecedented in American history."

"This President, by his tweets, has virtually no respect for the rule of law," Durbin said.

Last month, Republican Rep. Duncan Hunter of California, and New York Republican Rep. Chris Collins were indicted in a matter of just two weeks -- both politicians were two of Trump's earliest supporters in Congress. Both lawmakers have pleaded not guilty.

On Monday, Trump tweeted that two Republican congressmen were "brought to a well publicized charge, just ahead of the Mid-Terms, by the Jeff Sessions Justice Department."

"Two easy wins now in doubt because there is not enough time. Good Job Jeff," his tweet continued.

Sen. Mazie Hirono said she didn't think Trump understood the separation of powers.

"He thinks the attorney general works for him," the Democratic senator from Hawaii said. "He thinks the entire federal government works for him at his beck and call."

Democratic Sen. Pat Leahy of Vermont compared Trump's comment to North Korea, and noted his previous experience as a prosecutor.

"Only in — in North Korea the leader may say you may prosecute this person not this person. For the president of the United States to say, 'don't prosecute Republicans, only prosecute democrats,' - I was a prosecutor for eight years. Made my blood boil." Leahy said.

"This should concern every senator and every American and frankly hangs over this confirmation hearing for Judge Kavanaugh," he said.

Coons added that he is "confident" that special counsel Robert Mueller would "be looking at this particular tweet and ways in which the President is seeking to interfere with ongoing federal criminal prosecutions."

Trump's remark came just a day prior to the start of Supreme Court pick Brett Kavanaugh's confirmation hearing before the Senate Judiciary Committee -- where the question of how Kavanaugh would potentially rule on any issues dealing with the special counsel investigation and the president looms. Mueller is currently leading the investigation into Russian interference in the 2016 election. Trump has repeatedly denied any collusion.

Sessions, due to his role on the Trump campaign, recused himself from partaking in any investigations regarding Russian interference in the 2016 election, following his failure to disclose his own contact with the Russian ambassador while being confirmed by the Senate.

Due to his recusal, Deputy Attorney General Rod Rosenstein is overseeing the special counsel investigation. However, as CNN has previously reported, Trump has pressured Sessions on multiple occasions to reverse his recusal.

Blumenthal said that Trump seemed to be "deliberately trying to obstruct justice."

"So the justice system is under attack, and I'll be looking forward to statements from this nominee as a court of appeals judge, let alone nominee of the United States Supreme Court," he added shortly before confirmation hearings were set to begin for Kavanaugh.

Republican lawmakers have largely been silent or declined to weigh in on Trump's tweet.

"I don't speak for the President," Sen. John Kennedy, a Louisiana Republican, said Tuesday on CNN's "New Day." "He's entitled to his opinion, and maybe he thinks the policy ought to change. I haven't talked to him about it. I just know that I think it's important to have a consistent policy."

Sen. Lindsey Graham, R-South Carolina, said the tweet indicated Trump and Sessions "do not have a healthy relationship."

"I would say there's a general rule you don't issue indictments close to elections -- I think that's his point. But no Republican, no Democrat is immune from being prosecuted for misdeeds," he said.

He later continued: "I'm not suggesting these prosecutions are politically motivated, I'm not suggesting they're wrong. So what I am suggesting is that Jeff Sessions and the President do not have a healthy relationship."

"The United States is not some banana republic with a two-tiered system of justice -- one for the majority party and one for the minority party," Sasse said, adding later, "These two men have been charged with crimes because of evidence, not because of who the President was when the investigations began. Instead of commenting on ongoing investigations and prosecutions, the job of the President of the United States is to defend the Constitution and protect the impartial administration of justice."